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© ISO 2001 — All rights reserved
Table 8 — Options for well known type in service metadata
Services in the Catalogue are of a known type Services in the Catalogue maybe of an unknown type
Human is in the loop with the client
feasible Conceivably feasible assuming that the client interaction
is done with opaque messages, so there can be a generalized client that can create marked-up messages.
The human fills in the message based on the operations descriptions retrieved from the catalogue
Machine-to-machine. no human at the client
This is feasible if the Client implements a metamodel for the known service, in addition to the syntax for the
service. Questions if this is feasible.
7.6 Simple service architecture
The following simplifying assumptions should be considered when implementing a message-based architecture to support service chaining. Systems compliant to this set of guidelines shall be referred to as instances of simple
service architectures. Systems should comply with the simple service architecture.
• Message-operations. For simplicity it is desirable to model the operations as messages. A message operation
shall consist of a request and response. Requests and responses contain parameters as the payload, which is transferred in uniform manner independent of content. Simple applications are characterized by message
exchange patterns such as one-way or event, and two-way or synchronous request response interactions. A service specification should make such simple exchange applications as easy as possible to create and to use.
• Separation of control and data. A client controlling a service may not want the full results of the service. For
example, the user may have no need for the potentially voluminous intermediate products in a service chain. Only the final result of a service chain may be needed by the client. Therefore, operations of an interface
should separate the control of the service from the access to the data resulting from a service. A client should have the option of receiving just the status of an operation and separately the data should be accessible
through a separate operation.
• Stateful vs. stateless service. For simplicity it is desired that a service be stateless, i.e., that a service invocation be composed of a single request-response pair with no dependence on past or future interactions.
This will not always be possible. For some services, preconditions must be set and iteration may be required, then it will be necessary to model the service with a state diagram having multiple states. Transitions between
the states are triggered by operations.
• Known service type. All service instances are of specific service types and the client knows the type prior to
runtime. Clients shall contain software for accessing the service type prior to encountering service instances of the type in an implemented architecture. This assumption is that the client knows the service types.
• Adequate hardware. The services described in this International Standard are software implementations running on hardware hosts. This International Standard assumes that the issues of hardware hosting of the
software are transparent to the user. This is the assumption that the service has adequate hardware, i.e. hardware assignment is transparent to user.
8 Information viewpoint: a basis for semantic interoperability
8.1 Information model interoperability and the information viewpoint
To achieve information model interoperability is one of the main goals of the ISO 19100 series of standards. Many of the other standards in this series, i.e. ISO 19107, 19115 and others, are primarily focusing on defining the
content of the information that is being processed by the services and exchanged between services. The Information Viewpoint is defined in the ODP to include a static information model and a dynamic information model.
The semantics of service interactions, e.g. what services make sense to chain, are developed in 8.6.
© ISO 2001 — All rights reserved
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To be able to interoperate in the information viewpoint, two systems must be information model interoperable. To achieve information model interoperability the two systems must be both syntactically interoperable and
semantically interoperable:
Syntactically interoperable – Two systems are syntactically interoperable if they use the same structure for the information that flows in the systems and is processed by the systems.
Semantically interoperable – Two systems are semantically interoperable if they have a common understanding of the semantics of the information that flows in the systems and is processed by the systems.
The common structural models being defined by the information models address syntactic interoperability. In the ISO 19100 suite of standards the models are based on a generic feature model, which allows for representation of
various types of features, all having the same structure. To achieve semantic interoperability for feature types it is in addition necessary to match or make mappings between feature type definitions from feature type catalogues.
The issues of such information model interoperability will not be addressed in this International Standard.
The information viewpoint in ISO RM-ODP describes the information that flows in a system and is processed by a system. It focuses on the structuring of semantic information, typically the information that will be stored in a
database and communicated between the components of a system. An information model is used to describe the information viewpoint. This information model defines the structure and semantics of the information used in
system by defining objects, their properties and their relationships.
The information viewpoint is also concerned with the semantics of the information processing. Each particular service will need to define its syntactical interfaces through operations and its semantics through description of the
meaning of the operations and their legal sequencing. The latter can be done through pre- and post-conditions and invariants in OCL, and by UML state diagrams.
This section contains a description of a taxonomy of various services. There exist multiple possible taxonomies for services, based on various classification dimensions. The one that is used here is based on the extended OSE
model. The purpose of defining a taxonomy in this International Standard is to have one way of identifying geographic extensions to various existing service types. It is not intended to be the only taxonomy to be used in the
context of geographic services.
The work of identifying required services for geographic information standardization shall categorize if a needed service is GIS specific or more IT general, and which of the 6 service domains it belongs to. The processing
services domain will typically contain a variety of application-area GI specific services.
The next sections will describe typical IT Services and then show some possible geographic services in each of the six service domains.
8.2 Extended open systems environment for geographic services
The model for the information viewpoint is provided by ISO 19101. ISO 19101 defines the Extended Open Systems Environment EOSE model for geographic information. The EOSE defines classes of services based on
the semantic type of computation that they provide. EOSE provides the functional decomposition of the services for the geographic domain by extending the more general Open System Environment model [ISOIEC TR 14252].
Consistent with ISO 19101, this sub-clause defines six classes of information technology services that shall be used to categorize geographic services.
Human interaction services are services for management of user interfaces, graphics, multimedia, and for
presentation of compound documents.
ModelInformation management services are services for management of the development, manipulation,
and storage of metadata, conceptual schemas, and datasets.
WorkflowTask services are services for support of specific tasks or work-related activities conducted by
humans. These services support use of resources and development of products involving a sequence of activities or steps that may be conducted by different persons.
